This invention relates to a process for treating a well by injecting a reservoir-tailored combination of fluids which increases the effective permeability to aqueous fluids within a subterranean reservoir which communicates with the well.
Numerous types of well treatments have been previously proposed for effecting such a well stimulation. For example, the J. Reisberg U.S. Pat. No. 3,500,923, which relates to an oil recovery process, describes injecting a dispersion of about 5% by weight of a polyalkoxyalcohol sulfate surfactant in an aqueous liquid containing from about 4 to 5 moles per liter of sodium chloride and discloses that such a highly saline surfactant system is an efficient oil-displacing fluid--although one in which the salt content is reduced to from about 1 to 11/2 moles per liter is viscous but is inefficient for oil-displacement. The P. J. Raifsnyder U.S. Pat. Nos. 3,527,301 and 3,612,182, which also relate to oil recovery processes, describe injecting undiluted, or very concentrated, solutions of nonionic polyalkoxyalcohol surfactants (respectively, alone and in conjunction with a reservoir acidizing fluid) and disclose that such solutions are effective in causing a temporary selective plugging of the most permeable layers (or thief zones) of an inhomogeneous reservoir. U.S. Pat. No. 3,568,772, which relates to increasing the injectivity index of a well, describes injecting a micellar dispersion which contains less than 4% by weight (or less than 1.0 mole per liter) of an electrolyte such as sodium chloride ahead of an aqueous acid. U.S. Pat. No. 3,637,016, which also relates to increasing the injectivity of a well, describes injecting a soluble oil and water which contains less than about 1% by weight of sodium chloride. U.S. Pat. No. 3,946,812 which relates to an oil production process, discloses that injecting a polyalkoxyalcohol sulfate surfactant dissolved in an aqueous liquid in proportions providing . . . "a thickened, transparent, aqueous solution" . . . (column 3, lines 44 and 45) increases the sweep efficiency of a waterflood . . . "not by surfactant action but through the provision of a more favorable mobility and sweep of the reservoir" (column 3, line 68 to column 4, line 2). The H. J. Hill and D. R. Thigpen U.S. Pat. No. 3,712,377, which relates to an improved process for displacing oil within a subterranean reservoir, discloses that dilute aqueous surfactant systems should be tested regarding their tendency to form viscous emulsions when mixed with the oil within the reservoir and, if needed, an emulsion modifier, such as a lower alkanol, should be added to increase the ratio of the effective viscosity of the surfactant system to that of such emulsions.
Although such prior processes have been efficient in various individual situations, their efficiency is significantly affected by numerous physical and chemical properties of the reservoir and reservoir fluids--and those properties vary from one well to another. Thus, a formulation which is effective at one temperature is apt to be ineffective at another. A formulation which is effective with one reservoir oil is apt to be ineffective with another. And, further, the oil-displacing efficiencies are known to be affected by the rate of fluid injection, the composition of the water used for formulating the surfactant system, the composition of the water present in the reservoir interval to be treated, and the like.